docs: def immediateAssignment(ChannelDescription_presence=0,
                          PacketChannelDescription_presence=0,
                          StartingTime_presence=0):
      """IMMEDIATE ASSIGNMENT Section 9.1.18"""
      a = L2PseudoLength()
      b = TpPd(pd=0x6)
      c = MessageType(mesType=0x3F)  # 00111111
      d = PageModeAndDedicatedModeOrTBF()
      packet = a / b / c / d
      if ChannelDescription_presence is 1:
          f = ChannelDescription()
          packet = packet / f
      if PacketChannelDescription_presence is 1:
          g = PacketChannelDescription()
          packet = packet / g
      h = RequestReference()
      i = TimingAdvance()
      j = MobileAllocation()
      packet = packet / h / i / j
      if StartingTime_presence is 1:
          k = StartingTimeHdr(ieiST=0x7C, eightBitST=0x0)
          packet = packet / k
      l = IaRestOctets()
      packet = packet / l
      return packet